1. Field of the Invention
This invention relates to supported acid catalysts, their method of preparation and use in hydrocarbon conversion reactions, specifically isobutylene oligomerization reactions. The catalyst composition contains metal halides on a solid inorganic oxide support. The composition is prepared by reacting an adsorbent solid support containing surface hydroxide groups with organic metal halide wherein said metal is a single element selected from one of Groups IIA, IIB, IIIA, IIIB, IVB, VB, and VIB e.g., Al, under conditions sufficient for the organic metal halide to react with at least a portion of the surface hydroxyl groups.
2. Prior Art
Conventional Friedel-Crafts catalysts, e.g., AlCl.sub.3 and BF.sub.3, have been used extensively in many industrial processes as well as in the laboratory. The major drawback of these systems is the need to dispose of large volumes of liquid and gaseous effluents produced during subsequent quenching and product washing. Replacing these processes by those based on heterogeneous catalysis has environmental and economic advantages, e.g., ease of separation, catalyst recycling and elimination of quenching and washing steps.
The literature discloses efforts to anchor AlCl.sub.3 onto a solid support. Alumina can be chlorided with AlCl.sub.3, HCl, or Cl.sub.2. U.S. Pat. No. 3,248,343 to Kelly et al. teaches the treatment of surface hydroxyl-containing supports, e.g., alumina or silica gel, with aluminum halide and thereafter treating with hydrogen halide. Refluxing AlCl.sub.3 with solid supports, e g., silica, in chlorinated solvent, e.g., CCl.sub.4, is an alternate way of anchoring Lewis acid onto a support as disclosed in U.S. Pat. No. 4,719,190 to Drago et al and Getty et al., "Preparation, Characterization, and Catalytic Activity of a New Solid Acid Catalyst System," Inorganic Chemistry, Vol. 29, No 6, 1990, 1186-1192. However, these methods suffer from incomplete reaction between AlCl.sub.3, HCl or Cl.sub.2 and the support, resulting in catalyst that either contains a low concentration of the acidic species or is not very stable due to the leachability of physisorbed or chemisorbed AlCl.sub.3 species from the solid support. Krzywickl et al., "Superacidity of Modified Gamma-Al.sub.2 O.sub.3,"J. C. S. Faraday I, 1980, 76, 1311-1322 teach the treatment of alumina with a metal-alkyl species, e.g., CH.sub.3 AlCl.sub.2 vapors, to prepare a superacid catalyst which can catalyze the transformation of saturated hydrocarbons. U.S. Pat. No. 4,740,652 to Frame discloses an olefin oligomerization catalyst which comprises a porous support, e.g., silica, and plural metal components, an iron group metal, e.g., Ni, and alkyl aluminum compound, e.g., diethylaluminum chloride and aluminum halide, e.g., aluminum trichloride Such catalysts are used in transition metal catalyzed chemistry.
East German Patent DD225423 to Hallpap, et al. discloses a catalyst comprising alkyl aluminum halide supported on a silica support which is used for converting C4 isobutene-containing feeds to polyisobutylenes (PIBs). The catalyst is prepared from silica dried at 190.degree. C., and no initiator for cationic isobutene oligomerization is used.